1. Field of the Invention
The present invention relates to a device for detecting quality alterations in bulk goods on moving belt conveyors.
2. Description of the Prior Art
Through a publication by SYMONDS, D. F., 1991, "On-Line Ash Analysers Improve US Efficiency", MINTECH '91, pages 163 ff, Sterling Publications International Limited, London a device for determination of the ash content of bulk coal on belt conveyors is known, which by means of gamma ray absorption and backscatter measures the density of the material and, thus, indirectly the ash content of the coal. Devices of this kind have been marketed for more than 25 years by various manufacturers, as e.g. by the company "Laboratorien Prof. Dr. Berthold GmbH und Co.", Wildbad, Germany.
Analytically, these devices are hampered by measuring the density of a mixture of different matter only and, thus, can indicate indirectly only the amount of a certain component in simple mixtures.
The Finnish company "Outokumpu Electronics Oy" also markets devices of said kind, where the type "Beltcon 100" operates with gamma rays, while the type "Beltcon 200" is based on X-rays. The technical paper "Mining Journal", London, UK covered these devices in its issue of May 1991.
In general all above mentioned devices, which operate with gamma rays or X-ray fluorescence, have the disadvantage, that the radioactive sources used pose a health risk during maintenance and transport and that after their useful life have to be disposed of.
Devices for the determination of quality parameters of bulk goods on belt conveyors, which are based on the utilization of light of the UV to infrared range, sofar are not marketed in a commercial way.
From literature methods and devices are known, which use light beams of a defined wavelength to observe various matter, as e.g. country rock and coal in a mine, or individual components of goods on belt conveyors, as e.g. diamonds in ore from diamantiferous orebodies, or even tomatoes, and to provide information for directing, splitting or blending of material.
The German patent DD 293 748 A5 of the Martin-Luther-Universitat, Halle-Wittenberg of the year 1990 describes a "Verfahren und Vorrichtung zum Sortieren von Tomaten nach ihrem Reifegrad" (Method and Device for Sorting Tomatoes According to Their Ripeness). The use of a light source with a defined wavelength for the irradiation of tomatoes is disclosed, which depending on their respective degree of ripeness display photoluminescence of different intensity.
The published patent application DE 38 18 588 A1 of "Bergwerksverband GmbH", Essen, Germany of the year 1988 desribes a "Verfahren und Anordnung zur Unterscheidung unterschiedlicher Materialien" (Method and Device for Differentiation Between Different Matter). Here the use of one or various systems for irradiation and observation at defined excitation wavelengths and defined wavelength bands for observation to differentiate for example between coal and country rock is mentioned.
The two patent applications GB 2 219 079 A and GB 2 219 082 A by the company "Gersan Establishment" of Liechtenstein of the year 1989 disclose devices for concentrating diamantiferous ore, where the devices are specified having one light source operating at one defined wavelength and two or more receiver systems.
Already in the year 1980 the Canadian company "Scintrex Limited" of Concord, Ontario in the British patent GB 2 089 029 A gave a detailed description of a "Method and Apparatus for the Remote Detection of Certain Minerals of Uranium, Zinc, Lead and Other Metals". Here also one light source with one emitted wavelength or, for a multi-channel system, various light sources with one defined wavelength each for the excitation of photoluminescence are mentioned.
The Australian company CSIRO, "Commonwealth Scientific and Industrial Research Organisation", in 1989 applied for the U.S. Pat. No. 4,959,549 "Determination of Properties of Coal". The surface of coal on a belt conveyor is irradiated with UV light and the intensity of the photoluminescence is measured. A comparison of the measured signals with reference data leads to the determination of relevant properties of the coal. In this application also one light source with one defined wavelength is to be used.
It is known, that the intensity of photoluminescence depends on the wavelength of the excitation. These relationships are described in BROICHER, H. F., 1987, "Naturwissenschaftliche, technische und wirtschaftliche Aspekte bei der Entwicklung und Nutzung eines Photolumineszenz-Sensors fur die Rohstoffprospektion" (Scientific, Technical and Economic Aspects for Designing and Operating a Photoluminescence Sensor for Prospecting for Raw Materials), Verlag yon Dietrich Reimer in Berlin, Germany.
Therefore, for the precise determination of individual minerals or the alteration of the composition of a mixture of minerals it is desirable to operate at various wavelengths when exciting photoluminescence. Furthermore it is known, that the absorption and reflection at distinct wavelengths as well as the thermal inertia of minerals can be utilized for their respective determination.
According to the state-of-the-art, for each specific wavelength one light source is required, the light source preferentially being a laser. If the material shall be irradiated at various distinct wavelengths, then various light sources are required. Such a device will become very demanding regarding costs, space and energy consumption.